Configure Accumulo clients with HDFS root

When doing bulk imports, Accumulo clients need to retrieve a Hadoop configuration object with `fs.defaultFS` set. This is currently done by setting setting `$HADOOP_HOME/etc/hadoop` on the Java CLASSPATH. It would be nice if you could specify the following in `accumulo-client.properties` and avoid special configuration of your classpath.
```
dfs.root = hdfs://localhost:8020
```
Accumulo could still look for Hadoop config dir on classpath and build Hadoop Configuration object using it. It could override `fs.defaultFS` if `dfs.root` property is set when the client is created.

Start by tracing Accumulo client creation and the existing Hadoop configuration lookup from the Java classpath. Check how accumulo-client.properties is loaded and verify bulk imports with dfs.root set to hdfs://localhost:8020. Done means fs.defaultFS is overridden by dfs.root when provided, while classpath-based Hadoop configuration still works without special classpath setup.

Written by the indexing model from the issue text.